The effects of low-level x-irradiation during infancy will be studied on the development of postural and locomotor skills in rats. Ablation of the cerebellum during infancy (6 days) will be used as a structural control; exposure of the hippocampus to x-ray as an irradiation control. The morphological assessment of chages produced by irradiation of the cerebellum will be continued, with emphasis on electron microscopic-histochemical changes. The lasting motor deficits of adults will be determined to assess the extent of recovery of function. The effects of x-irradiation of the hippocampus during infancy will be examined with morphological, physiological and behavioral techniques. This will include specification of cell loss (especially dentate gyrus granule cells) with different schedules of irradiation; alterations in hippocampal electrical activity in different behavioral states (rest, locomotion, sleep); changes in running during day and night, in aggressive and maternal behavior, and in several other behavioral situations. Work will continue on the morphological and behavioral assessment of the effects of mild and severe gestational or lactational undernutrition.